Method and composition for coating iron and steel articles



Patented F 1 939 'uN 'rEo STATES,

PATENT OFFICE] No Ilrawlmr. Application February 25, 1937, Serial No. 127,808

5 Claims. (01. Lia-a5)- This application is in part a continuation of our copending application of the same title, Serial No. 926 filed January 8th, 1935. By this reference thereto, the entire disclosure thereof is .:5 hereby incorporated herein.

This invention relates to methods and com-- positions for suriace'treating iron and steel articles with an. aqueous solution containing an alkali 'and'an oxidizing agent, for coloring or 10 coating the articles by chemical action on the surface thereof, and has for its principal objects the development of a very simple and economical aqueoussolution for coating or coloring'ierrous metals chemically,'and a definitemethod of control of the solution during plant operation.- This invention has for other objects to avoid a large number of the following dis advantages which have rendered'prior expedients along this line unsatisfactory:

The prior coatings have been defective in durability or appearance, being non-adherent or subject to chipping,'cracking, scaling, peeling or powdering off, ipr imable to withstand stamping, shaping or rolling operations, or non-rust resisting, or the coating has been dull orlacking beauty and depth, or not permanent, or subject to discoloring with timer The prior processes have been expensive in the cost to color a unit area, requiring costly equipment or electric set-up and power, or difficult or complicated, requiring more than one operation to complete the work such'as spraying, baking, plating or hand sponging or requiring expert and skilled labor, or being incapable of coloring large quantities in baskets, or yield- .fing non-uniform resultsor altering dimensions or affecting hardness and elasticity of-articles particularly special steels being treated.

The baths employed heretofore have required 40 expensive chemicals or high temperatures or molten salts or inflammable materials; or have been dltllcult to prepare or may decompose on standing idle, or have short life in operation, or leave a scum or-tacky or greasy surface on 46 the article or attack the surfacesuch. as by etching the polish, or deposit oxides of metals electronegative'to iron thusdecreasing rust resistance, or generate excessive carbonaceous material which interferes with operation, or the so bath will not work on common grades of iron orsteel.

or all these 'dlsadvsirltaesbf as prior ex pedlents along this line, perhaps the greatest or most diillcult to-master is that the solution ceases to motion properly after a comparatively small interfere number of articles of. ferrous metals have been coated or colored, even before the oxygen or color supplying content of the bath has been exhausted. "This we have found to be due to the presence of some formsor compounds of iron 5 resulting from previous operation. Such forms or compounds are frequently formed when plain water is added to replace evaporation losses, and they are generally colloidal in nature. a

It is therefore a particular object of the pres- 10 e'ntinvention to avoid the formation of such undesirable forms or compounds of iron resulting from previous operation, so as to prevent them. from interfering with the'further operation.

We attain long life for our coloring bath by 15 application of one or more of the following conditions: Q

(1) .Control of the original composition of the solution or bath, including the optional use of inert water soluble and alkali soluble chemicals 2 in place of a considerableproportion of the alkali. (2) Control of the temperature of operation, including the optional use'of special ranges'for. different color effects. l

(3) Addition of make up water ;to replace 5 evaporation losses in the form of a relatively dilute aqueous solution of alkali or oxidizing agent, or both.

With regard to the alkali to be used according to'the present invention, we have found that 30 we can use any-water soluble, non-volatile alkali or combination of alkalies, such as, for example,

sodium hydrom'de, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, sodium borate or sodium phosphate. These 35 examples are given in an illustrative and not in a limiting sense.

with regard to the oxidizing agent for our purposes we have found that we can use any material which will form an oxidizing radical 40 or substance on the bath, such. as for example,

a chlorate, nitrate, nitrite, ,oxide, nitrophenol,

chromate, nitroprusside of any metal or element,

but preferably the alkali metals, although the examples are given in an illustrative and not all inalimitlngsense. V The 'revivifying, activating or regenerating agents which we have: found to be suitable for our purpose are for example a cyanide, tartrate, bitartrate or tannate, or any other substance 50 capable of forming complex ions with that type of iron compounds shown to act as poisons or with the coloring or coating action in the coloring bath, and hence the examplesare given in an illustrative and not in a umiunc u oesreescandcan inactive due to the'presence orthelmdesirable' form or compound of the iron which has come into the solution mm the articles previously The temperature fmm'105 to 180 be attained, it n,

adding to the treating solution into:- and alkali soluble salts such as, for example, sodium chlo- The following is an example indicating the composition 01' our bath:

Alkali 0.3 to a 16s., preferably 3 lbs.

Oxidising agent 0.004 lb. to 10 lbs, preferably wsteruhs.

V ings.- l'br eaample,

81113, for

to function. The concentration of this inert salt may vary from O'to 00% oi the total weight oi the bath. The iron or steel articles are immersed in the bath for aperiod of fl've'seconds to thirty minutes, on the depth of coating desired, and the character or the iron or steel being treated.

Ai'tercoatingadeflniteamountotmetalitis sometimes desirable to add a small amount of example, about 0.5% additionbyweightotthebath,toenablethebathto continue; to function satisfactorily for the'coat ing.- This addition permits a further definite amount ofmetal tobe coated. after which a furaddition or either activating salts or make materials must be added. This process can continued practicallyindeflnitely, thus permitting continuous operation of the bath. There are definite limits to-the amount'ot activaflng' salts-which can be added to the bath-at'any 7 one time in order for the same to function-properly. I

'Ihecompoaition o! the bath can be varied over a broad range and still yield-satisfactory coatthe concentrations or the various ctlnponents'of the bath, except the activating salts, can. be

by evaporation during operaoitm though not always lost its adoring powers: To restore the coloring powers,

atently potassium chloride. etc. in order to atbriei'timein-p tions, while before .cated. Thereis'anap it was to either raise the operating temperature. or to add a regenerating agent. On caremlinvestigation of this phenomenon taking plat when water is added to this type of bath,

it was learned that, the water added reacts with the insoluble ironsalts present (which were formed during previous coloring action of the bath O11 iron and steel the cause of the bath to become pomoned and stop its coloring action. The formation of this,

colloidal. iron compound was shown by the fol lowing experimentz- A bath consisting of caustic soda, sodium nitrite, and water was operated without resort to regenerating agents. Aiter coloring a large amount of steel articles it was decided to filter the solution through asbestos in order to free it from a heavy insoluble green sludge consistingoi the iron salts formed during coloring operations. Although the filtrate was perfectly clear and practically colorless, the washings of e green iron salt sludge, obtained by pouring 'coldwater over the filter funnel containing the sludge, were a rich red brown color. These s on standing afew minutes yielded a fluocculant red brown precipitate suspended in a colorless solution, very similar to the characteristic red brown precipitate often observed when a colloidal solution of ferric hydroxide breaks up into like constituents.

As a result of these observations a series of tests were made with a bath composed of an alkali, water, and nitrite. This bath was operfated without using regenerating agents, and the losses due to dragout of bath by the work'and to evaporation were replaced from time to time by a .weak solution of alkali plus nitrite. Using this manner of replacing bath losses, it was possible to obtain perfectly. satisfactory-coloring results,-

and a long litei'rom the bath. If plain water were used toreplace bath --in above tests, the solution would have a veryshort life. This fact has been proven innumerable times in both laboratory experiments and in plant scale operathis particular discovery we had found it necessary to'add a regenerating agent from time to time to prolong the lii'e.oi' the bath. 7 v

. The following table gives the data which was taken in experiments supporting the above statements. Noregenerating'age'nt was used in these experiments, and bath losses-were replaced by a 10% solution of alkali phis'nltrite:

Operating ual NaOH who, Hi0. mum a"; 3:5 3m

(min) colored Grains Grant Gram "G.

no 10 v 240 {140-156 5 0 Good. no (lo-a0) zao 111- 46 5 a Good. itsv 10 too 5133-15! sas Good. 10 10 .aoo z-m- .s cm.

' The amounts given in the column oi square feet of steel colored size oiv bath obtainable.

represent amounts colored in given and are not the maximum as operating conditions. or the bath to those indipreqabiywider'algeot practicallyallthe factors involved. 2.

Notonlydowerccosnisethetactthatthe colloidal type oi.- iron compound. To 1 this lattertcompound or perhaps its reaction with the normal constituents of the bath we attribute.

addition of plain water to this type of bath is. harmful to its coloring action, but also we appreciate the fact that in entering articles to be colored into the bath, the former should not have plain water on them but preferably should be dipped in a dilute solutionof caustic. soda, or

caustic soda plus nitrite, immediately before enrinse in cold water, dip in an acid pickle, ,rinse in cold water, dip .in a cold or hot 10% solution of caustic soda or a cold or hot solution containing grams per liter of coloring salts (alkali plus oxidizing agent), the ratio of alkali-to oxidizing agent being the same as in the coloring bath. Now, without rinsing, enter into the coloring bath at the proper operating temperature which may range from to 165 C. for approximately five minutes. Remove from bath, rinse, and dry. Articles can often times be colored satisfactorily even when entered into bath without any preliminary treatment.

Thus wehave made an improvement in the operation of a ferrous metal coloring bath such that regular and continuous coloring operation can be attained without the use of regenerating agents, the bath being operated substantially as above described, and resulting in a prolonged life of same. i I

We have also discovered the detrimental action of plain water added to a used coloring bath composed of alkali, oxidizing agent and water, and the remedy for same, namely addition of a relatively dilute solution of alkali, or alkali plus oxidizing agent to the bath in place of water. 7

restrict ourselves to the above listed inert water I soluble chemicals nor to the amounts used as experience has shown that a wide list; of these can be used with equally satisfactory results.

- By increasing theconcentration of chemicals in the bath andincreasing-the operating temperature, an interesting and valuable new coating on iron and steel is obtained. This coating.

is an .olive green etching on the surface of the metal. It is very adherent and will absorb unvarnish, due to the etched nature of the coating. This type of surface results in greater protection of the steel from rusting elements for it acts as an ideal and strong bond between the metal and any lacquer, paint, or varnish put over it. Also, as it is'capable of absorbing more oil due to the etched nature of the coating, a .better rust' protection is afforded whenthe colored article is oiled.

The following is an example showing the conditions required to obtain this olive green coating on steel or'lron: v

' wratin N aO'H NaN 0; H O temperapg Color ture I o Grams Grams Grams 0. Min.

750 250 600 156-225 5 Olive green.

In general we may say that to get the olive "green coating, a high concentration of chemicals in solution is necessary, but the operating temperature and coloring time may. vary over a very .wide range.

Our work to determine the effect of varying concentrations of oxidizing agent shows that even lower concentrations can be used and still ob tain coloring action from the bath. The following data was taken from our experiments along these lines:

. Operat- Rfi NaOH NaNO; 11,0 ing teingg? NaCN Color on steel perature Grams Gram Grams C'. Min. Gram: '1 250 0.6 800 5. I 0 Gray etch. 2 250 2 300 140 ls 0 Gray, a 260 5 300 140 o 0 Black.

4 250 so 300 143 L 0, Do. 5 140 560 240 a 0 Do. o 140 560 240 155 54 '5 Rich blue. 1

We have also found 1t to be possible to replace We claim:.

a considerable proportion of the alkali in the type of bath outlined herelnbefore by inert water soluble chemicals without harming the coloring powers of the bath. The following data was taken during experimentsalong these lines:

For economical reasons or otherwise it may be "advisable to replace part of the alkali with an inert chemical and for these reasons we made the aboveexperiments and disclosures. We do not 1. Method of surface treating ferrous metal articles, which comprises subjecting them to surface contact with a relatively concentrated aqueous solution containing an alkali and an oxidizing agent and having a specific gravity within the range of 1.30 to 1.60 measured at 120 C., while maintaining said treating solution at a temperature of from 105 C. to C., whereby chemical action takes place on'the surface of said articles,

.. usually large amounts ,of oil, lacquer, paint, or

and avoiding inhibiting action of products resulting from such operation and attendant upon the addition of plain water to said concentrated solution; by adding to said treating solution to make up. water losses due to evaporation, a relatively dilute aqueous solution of the order or10'% of at least one of the substances of the group named above as constituents of said relatively concentrated solution.

2. Method of surface treating ferrous metal articles, which comprises subjecting them to surface'contact with a relatively concentrated aquesolution containing an alkali and an oxidising agent having a specific gravity within the 1 to 1.00 measured at 120 C. while solution at a temperature of to 180 (2., whereby chemicalastion surface of said articles, and action '01 products resulting from such operation and attendant upon the adof plain water, by adding to said solution to make up wa losses due to evaporatiom a relatively dilute aqueous solution of the order of 101, 0: at least one substance of the group consisting of alkalis, oxidizing agents, and activating agents'which chemically convert such products into substances harmless to the treating powers of the relatively concentrated solution.

3. Method oi surface treating ferrous metal articles, which comprises subjecting them to surface contact with a relatively concentrated aqueous solution containing an alkali and an oxidizing agent and having a speciiic gravity within the range of 1.30 to 1.60 measured at 120 0.,

dition of plain water to-said concentrated solution, by adding to said treating solution to make up water losses due to evaporation, a relatively dilute solution of the order of 10% of at least one oi the constituents of said relatively concentrated solution.

4. llethod'of mm treating ferrous metal articles,toproduceanolivegreenetchingon their surfaces, which comprises suhiectingthem tosurfacecontactwithan ammiss'olutioncontainingacausticalkaliandanalklllmetalni: trate,-the weight of alkali and oxidizing agent beinginexoess oftheweightoiwater,andmaintaining the temperature of said treating solution between 156 and 225 C. whereby chemical action takes place on the surface of said articles. simultaneously etching and coloring the same.

' 5. Bath for surface treating ferrous metal articles, comprising a relatively concentrated aqueous solution containing an alkali and an oxidizing agent and having a specific gravity within the range of 1.30 to 1.00 measured at C., and adapted to act chemically on said articles when maintained at a temperature of from 105 C. to 180 C., but which would become ineiiicient due to inhibition oi iron ions accumulating from said action if and when plain water were added thereto to make up'evaporation losses, in combination with a pre-dip bath comprising a relatively dilute aqueous solution of the order of 10% of at least one of the chemical constituents of the treating bath, and adapted to receive said ferrous metal articles in advance of treatment and thereby prevent drops of plain water from clinging to the articles and being carried into the treating bath, said pre-dip bath also being adapted to make up evaporation losses from said treating bath and thereby avoid necessity of plain water for that Purpose, and consequent in hibition of the action of the relatively concen-- trated treating bath.

MARK WEISBERG. LOUIS CORMAN. 

